Guide catheters are used to gain access to the desired target location within the vasculature of a patient and provide a safe, smooth conduit to guide and support another device, such as an interventional catheter, to the target location. A guide catheter is typically inserted into the body through an introducer sheath and over a guidewire. Guidewires are long coiled wire structures that can be navigated through the vasculature and then used to lead another device through the vasculature. The guided device is typically the delivery device that carries an implant for deposit in the vasculature, an active device that carries out the diagnosis, therapy or intervention. Guide catheters can also be used to pass fluids for visualization, diagnosis or treatment.
A sheath is a type of guide catheter that also seals the entry point in the vascular space. The sealing is usually accomplished with a valve on the back of the sheath that either passively opens and closes when devices are inserted into it, or is opened and closed manually by the doctor when a device is inserted into it. The sheath protects the vessel from damage that might be caused by the guide or device that is passed within the sheath. Sheaths are typically thinner-walled and more flexible than guide catheters. They are typically straight-ended and may be inserted into the vessel over a guidewire or an introducer/obturator. An obturator/introducer is typically a long plastic tube with a distal tapered end that is longer than the device into which it fits and contains a central lumen to track over a guidewire. The obturator is usually flexible enough to allow the insertion of the device over it into a vessel or through a hemostatic valve and rigid enough to straighten out any pre-shaped guide that is over it.
Over the years, many guide catheters have been developed for treating specific diseases, delivering specific devices, or for accessing specific locations within the body. These guides are typically PTFE lined devices with walls made from a composite of thermoplastics and metal wire braid and coil reinforcements. They are thin-walled and flexible, but can transmit some torque from the proximal end to the distal end to allow the doctor to steer the distal end to the location of interest. Most guide catheters have a specific pre-formed shape that allows them to perform their narrow function and only their narrow function. They have been developed and customized over the years to reach one specific anatomic location only. The variety of achievable shapes is also limited because the guide must be inserted into the body in the straight configuration, so that the guide can be advanced to the location of interest without dragging or scraping along the vessel walls. Once at the desired location, the guide typically retakes its shaped configuration when the obturator or guidewire is removed from it. This flexibility detracts from the guide's ability to support interventional devices that are inserted through it. Also, the curvature of a pre-shaped guide must be limited, or it will not straighten out when the obturator is inside of it. These limitations of fixed shape guides point to a need for improved devices to enable atraumatic access to the target locations of interest.
A typical use of these devices is in interventional cardiology to treat a plaque build up or blockage in a patient's coronary artery. These blockages can lead to heart attacks and death. Typically, a patient presenting with symptoms is investigated with EKG tracings, a stress test or angiography (imaging with moving x-ray pictures and radiopaque fluids). In order to complete an angioplasty, the doctor would locate a femoral artery under the skin in the groin and install a sheath into an arterial opening, such as an 8 French sheath. The distal end of the sheath stays inserted into the artery and the proximal end, which has a hemostatic valve on it, remains outside the body. The surgeon would then insert a guide catheter that has a guidewire inside it through the sheath and into the femoral artery. Visualizing the devices on fluoroscopy, the surgeon manipulates the tip of the guide and guidewire retrograde up the aorta until he can engage the ostium of the coronary artery that has the suspected blockage in it. The surgeon then advances the guidewire into the artery toward the lesion of interest. After identifying the lesion location with angiography, the surgeon introduces an angioplasty balloon catheter into the guide (may or may not be over the guidewire inside the guide) and advances the angioplasty balloon to the lesion site. When correctly located, the surgeon inflates the balloon on the end of the angioplasty catheter to push the plaque back against the artery walls, thereby alleviating the blockage in the vessel. Once the procedure is completed, he removes the angioplasty catheter, guide, guidewire and sheath and disposes of them. The procedure for implanting a stent in the body is very similar to the previously described angioplasty procedure. After inflating a balloon to push the plaque against the wall of the vessel, the doctor inflates or expands a stent, which is left permanently behind in the vessel.
Interventional cardiologists now have procedures and different specifically shaped guides for the left and right coronary arteries, renal arteries, carotid arteries, internal mammary arteries, abdominal aorta, hepatic arteries and veins, pulmonary arteries, and veins, the atria and ventricles of the heart, mesenteric arteries, femoral arteries, neurological locations, and the coronary sinus of the heart. In many of the procedures, the fixed shape of the guide is not quite right for the patient anatomy and the surgeon must wrestle to get the guide into position, or discard the guide and try another shape. This consumes significant time in the catheterization lab which has costs today that run roughly $20 per minute. Although fixed guide catheters are relatively cheap medical devices today, the inability to access a target site in the body quickly due to anatomical variation or the propagation of disease can quickly cost hundreds of dollars. Extensive time in a fluoroscopy suite also exposes the physician and the patient unnecessarily high doses of radiation.
There are a small number of new guide catheters whose shape can be changed by the operator during surgery. These are called deflectable guide catheters. Their shape-changing ability allows them to be adjusted by the surgeon during a procedure to fit the anatomy of the patient, which normally varies due to disease, body type, genetics and other factors.
For example, Badger, Guiding Catheter With Controllable Distal Tip, U.S. Pat. No. 4,898,577 (Feb. 6, 1990) and Badger, Guiding Catheter With Controllable Distal Tip, U.S. Patent, U.S. Pat. No. 5,030,204 (Jul. 9, 1991) describe a steerable guide catheter with and outside diameter of 0.118″ and an inside diameter of 0.078″. A number of US, European and Japanese patents issued to Lundquist including U.S. Pat. Nos. 5,685,868, 5,228,441, 5,243,167, 5,322,064, 5,329,923, 5,334,145, 5,454,787, 5,477,856, 5,685,868, EP521595B1, JP 7255855A2, describe the use of slotted metal tubes such as nitinol torque tube elements in steerable catheters. Rosenman, Drug Delivery Catheters That Attach To Tissue And Methods For Their Use, U.S. Pat. No. 6,511,471 (Jan. 28, 2003)(the entirety of which is hereby incorporated by reference) describes a steerable guide catheter for delivering a medical device within the ventricle of the heart using the slotted Nitinol torque tube technology of Lundquist with a relatively large catheter lumen as it was used to pass other medical devices.
Qin, Deflectable Guiding Catheter, U.S. Pat. No. 6,251,092 (Jun. 26, 2001) describes a deflectable guide catheter whose deflection point is proximal from the distal tip. This patent does not enable a tight radius bending deflectable guide catheter that can track over a guidewire to locations of interest in the vascular tree in patients.
Farmholtz, Torgueable And Deflectable Medical Device Shaft, U.S. Pat. No. 6,716,207 (Apr. 6, 2004) describes a steerable catheter with slits in a tube component in the shaft. However, the bending point of this catheter is proximal of the end of the catheter, which results in a large sweep distance during bending, which is not desirable. Also, this catheter has a stiffer braided portion distal to the bending section, which decreases the trackability of the catheter. Also, this patent does not enable the construction of the shaft with a large central lumen or detail the cross sectional construction.
The ideal guide catheter is one that can adjust for varying patient anatomies while maintaining a thin wall and providing enough support for the devices passed through it to their target locations in the body. It should be smooth and lubricious on the inside and the outside surface. It should be stiff enough in torque to allow the doctor to direct the distal tip by manipulating the handle outside of the body. Minimizing the outside diameter of a guide catheter is important to minimize the size of the opening made in the patient's vessel to gain vascular access, and also to enable the distal portion of the device to be advanced through smaller vessels. Smaller openings are easier to close after the procedure and have less post-procedure healing complications. It is also important to have a large internal diameter in a device to allow easy passage of other interventional devices. The ideal guide catheter should be compatible with commonly used interventional guidewires, angioplasty balloon catheters, stent catheters and hemostatic introducer sheaths. The ideal catheter should also be visible on fluoroscopy and usable in an MRI suite.